1. Field of the Invention
The invention relates generally to data display systems and more particularly to data display systems of the kind commonly known as bar graph displays in which an indicator line of the display represents the numerical value of an analog input signal amplitude.
2. Description of the Prior Art
Generally, prior art analog bar graph display devices have, on the one hand, employed cathode ray indicator techniques such as those of the kind described in the Bialkowski et al U.S. Pat. No. 3,248,650 for a "Cathode Ray Tube Indicator for Displaying Plural Input Signal Values", issued Apr. 26, 1966. While such arrangements find utility where a plurality of bar graphs is to be displayed side-by-side for mutual comparison purposes, cathode ray tubes, by their inherent nature, occupy considerable volume, extending well behind the face of the display and also undesirably require high voltages for electron beam acceleration and deflection purposes.
On the other hand, there are prior art electroluminescent bar graph displays utilizing arrays of electrically stimulatable light emitting diode elements which have met with some success. While such individual bar graph display devices may be placed in side-by-side relation, the resultant assembly still does not satisfy entirely needs for more compact and efficient displays. Even when used singly, more compact devices are in significant demand. Many prior art electroluminescent bar graph devices also are characterized by a built-in lack of flexibility of use, the entire display element being offered in integrated form so that the display designer's effort is severely confined by limitations thereby imposed. For example, recent displays, such as those of the Joline U.S. Pat. No. 3,221,169 for an "Electroluminescent Graphical Display Device", issued Nov. 30, 1965, and of the Yiotis U.S. Pat. No. 3,275,871 for "Display Apparatus", issued Sept. 27, 1966 are representative of such integrated display devices. These two patents are also assigned to Sperry Rand Corporation and additionally illustrate a trend in the art toward the use of complex logical control circuits made necessary by the nature of the displays.